Giant Scale 3D Plane Scrathbuild

[Pieliker96]

Why is there a separate battery for servos and recievers, wouldn’t adding a BEC allow you to use only one main battery and shave a few pounds?

If I had to guess, the servos probably gulp power - probably on the order of a couple amps per servo under full load. Adding a high-power BEC off the main batteries would work, but it adds another failure point. Using separate batteries for the propulsion and flight controls adds fault tolerance in the event of losing the propulsion power system and also allows the flight controls to be powered up independently of the motor on the ground for safety and convenience.

 

[ThomasMartino]

Why is there a separate battery for servos and recievers, wouldn’t adding a BEC allow you to use only one main battery and shave a few pounds?

Good question.

I don’t know of any 150 amp ESCs that come with a BEC. But even if I had one, I would still use dedicated batteries for the receiver and servos for safety. Redundancy is important on big planes.

I’m using high voltage servos that need power directly from a 2S lipo to produce their maximum torque. Using a regular 6V BEC would reduce my servo torque from 444oz-in at 8.4V to 278oz-in at 6V. One of these servos can draw up to 6 amps if it stalls, and I’m using five of them. A servo failure in flight will drain batteries very quickly. Using two 2,200mah batteries to power them guarantees that if a servo stalls I will have enough power to get my plane back without a radio brownout.

 

[ThomasMartino]

If I had to guess, the servos probably gulp power - probably on the order of a couple amps per servo under full load. Adding a high-power BEC off the main batteries would work, but it adds another failure point. Using separate batteries for the propulsion and flight controls adds fault tolerance in the event of losing the propulsion power system and also allows the flight controls to be powered up independently of the motor on the ground for safety and convenience.

You’re exactly right. These servos are monsters. They easily draw over an amp in normal operation, and over 6 amps when stalled. With five of these things eating up power I want to have plenty of battery capacity and redundancy. Plus they need the higher voltage to produce their max torque for a demanding application like this.

 

[ThomasMartino]

I started working on the wing spars. They are made of unidirectional carbon fiber and Sitka spruce. Massive overkill I know...

The lamination is 9 layers of uni carbon, each one shorter than the last. The layup was wet out by hand, then vacuumed bagged with plenty of bleeder to absorb the extra epoxy. The cured laminate was then cut into 1/2” wide strips. I want the carbon fiber to taper, but the overall thickness of the spars needs to be an even 1/8”. All I had to do was flip them over and run them through a planer to remove the extra spruce. Here is a photo that shows how thick the carbon is at the root versus the tip.

 

[ThomasMartino]

I want to make molded carbon fiber leading edges for the wings, so I started making a plug to form the mold from. Once the fiberglass cures I will paint it with duratec surfacing primer and polish and wax it. This thread is going to be about 50/50 composites work and balsa building from here on out.

 

[ThomasMartino]

That’s all I have to share for now. I’ve been busy the last few days so I haven’t gotten much work done on this build. I spent all day yesterday helping my dad prepare his full scale plane for repainting.

 

[whackflyer]

That’s all I have to share for now. I’ve been busy the last few days so I haven’t gotten much work done on this build. I spent all day yesterday helping my dad prepare his full scale plane for repainting. View attachment 190150 View attachment 190151

What is the plane?

 

[Pieliker96]

What is the plane?

I originally thought it was a Thorp T18 from the canopy, but it's got a good bit of wing taper and that flap that continues under the fuselage. I had some looking around for similar kit aircraft without any luck before looking closer and finding the N number on the panel - N355JM is a Mustang Aeronautics Mustang II.

 

[ThomasMartino]

I originally thought it was a Thorp T18 from the canopy, but it's got a good bit of wing taper and that flap that continues under the fuselage. I had some looking around for similar kit aircraft without any luck before looking closer and finding the N number on the panel - N355JM is a Mustang Aeronautics Mustang II.

Good eye! That’s a Thorp canopy on a Mustang II. My dad build this plane in the garage when I was a toddler. It has a 200hp Lycoming engine upgraded with high compression cylinders. He used to race it in the sport air racing league. The old purple paint was getting pretty worn so we are sanding it off and painting it orange. One day I will build a 1/3 scale model of it, but I have too many projects in the queue right now.

 

[whackflyer]

Good eye! That’s a Thorp canopy on a Mustang II. My dad build this plane in the garage when I was a toddler. It has a 200hp Lycoming engine upgraded with high compression cylinders. He used to race it in the sport air racing league. The old purple paint was getting pretty worn so we are sanding it off and painting it orange. One day I will build a 1/3 scale model of it, but I have too many projects in the queue right now.

Cool! I saw a mustang 2 painted like a Corsair at our local fly-in once.

 

[ThomasMartino]

Last week was pretty busy for me, but I made up for it by working on the plane all weekend. I’ll be in the shop again all day today so there should be lots of updates to share.
The first step was finishing the mold for the wing skins. I sanded the plug and waxed it before brushing on a coat of orange tooling gel coat. Things got messy quick so I don’t have any pictures of the mold layup. It was a few layers of thin fiberglass cloth followed by a couple layers of fiberglass chopped strand mat. It’s not the prettiest or best mold, but it’s fine since I only need to produce two parts with it.

 

[ThomasMartino]

While that was curing I finalized some CAD stuff for the wing ribs. I use Compufoil 3D and AutoCAD.

 

[ThomasMartino]

Framing up the wings is the easy part. Each wing took about half an hour to assemble. When building large wings I like to weigh each sheet of balsa and select certain densities for certain ribs. I used the hardest balsa I had for the root ribs since they will hold the retaining bolts. For the rest of the ribs I used medium to extra light balsa. The tip rib being the lightest. This is a habit I got into from building sailplanes. For a sailplane to thermal well you need to minimize yaw inertia. A good way to do that is to build the tips of the wings as light as possible. If most of the mass is centered near the CG the glider will be much more nimble and can safely turn tightly in small thermals.
For a 3D plane yaw inertia is both good and bad. Having less yaw inertia will make the plane much more responsive to control inputs, but too little yaw inertia will make some post-stall tumbling maneuvers impossible. The tail feathers on my plane are pretty heavy, and the composite wing skins are going to span load the wings, so I think this plane will have more than enough mass at the extremities for any kind of tumbling maneuver. I didn’t do the math though, so only time will tell.

 

[ThomasMartino]

Bonus points if you know what kind of composite reinforcement fabric this is.

I did a couple test runs and found that laminating the balsa skin right onto the composite fabric in the vacuum bag usually resulted in the fabric creasing around the edges of the balsa sheet. To alleviate this problem I wet out the fabric with fast curing laminating epoxy and vacuum bag it first without the balsa. After two hours I remove it and add the balsa sheets. Here’s a photo of the fabric in the mold after removing it from the bag. I used perforated release film rather than peel ply. This allowed me to carefully remove the assembly from the bag without disturbing the partially cured fabric in the mold.

Then I glue the balsa sheet on with gorilla glue and vacuum bag it again to hold it tight. This doesn’t require release film or bleeder ply, so it’s quick and easy.

After letting the completed layup cure for a few more hours I had a perfect part.

 

[ThomasMartino]

While the wing skin was curing I built the vertical stab. This was a fun part to make. I had some carbon fiber and spruce spar material left over from the wings, so I cut it down to size and used it for the main spar of the stab and rudder. I used extra light balsa for the ribs. All 11 of them weighed less than an ounce. This gave me some wiggle room in the weight budget to use heavier, stronger, balsa for the rudder skin. In addition to using strong wood, I also sheeted the rudder on a bias. Angling the grain really increases the torsional strength. I don’t want the rudder to have any flex as this could result in flutter. I used light balsa to sheet the stabilizer since this part is already plenty strong enough thanks to all the spars. The next step will be cutting the rudder off and adding beveled pieces and hinges.

 

[Bricks]

Great job sssoooo what is the gray composite for the leading edge? All most looks like a carbon fiber matting.

 

[ThomasMartino]

Great job sssoooo what is the gray composite for the leading edge? All most looks like a carbon fiber matting.

It’s spread tow high modulus carbon fiber and Zylon blend. The pictures don’t do it justice. It has a beautiful golden bronze color. Zylon has a better strength to weight ratio than carbon fiber so this is an exceptionally strong and lightweight fabric.
I will be using this on the horizontal stabilizer as well. The cowling will be made with a regular 3K 2x2 twill carbon fiber and Zylon blend

 

[ThomasMartino]

I love working on small details like this fillet between the vertical stab and fuselage.

 

[hsquier]

It's beautiful.

To me a piece of art.

PS : On first photo last post 07:06 PM, at the back above the purple plane : do I see a Profile Wildcat ? (sorry it's my topic).

 

[ThomasMartino]

Thanks! I’m glad you like it. Not a Wildcat. Those are some 3D profile planes I built.